To improve assembling ability and to reduce a cost by a method wherein a high thermal conductive deicing member to prevent the occurrence of dew condensation and icing to the nozzle hole of a fuel injection valve is arranged at the mounting port part of an intake manifold with it protruding internally of the intake manifold.

A high thermal conductive cylindrical deicing member 20 is inserted in the mounting port part 12 of an intake manifold 11 from above, and the flange part 20a of the deicing member 20 is hooked at the lower end step part of the large part 12a of the mounting port 12. The lower end part of a fuel injection valve 13 is inserted in the mounting part 12 from above, the seal member 19 of the fuel injection valve 13 is pressed in the large part 12a of the mounting port 12 and forced into contact with the flange part 20a of the deicing member 20. This constitution seals a space between the fuel injection valve 13 and the large part 12a of the mounting port part 12 with a seal member 19, assembles the lower end part of the fuel injection valve 13 at the mounting port part 12 of the intake manifold 11, and assembles the deicing member 20 at the mounting port 12 by nipping the flange part 20a of the deicing member 20 between the lower end step part of the large part 12a of the mounting port part 12 and the seal member 19.